SMD Beads and Chokes Introduction 1.0 INTRODUCTION 2.0 EMI INTERFERENCE During the design phase, problems with SUPPRESSION AND EMC interference can be avoided to some To support designers and manufactu- ELECTROMAGNETIC extent. Often additional suppression rers of electronic circuitry, FERROX- COMPATIBILITY components such as capacitors and CUBE manufactures a comprehensive inductors will be necessary to meet the line of ferrite EMI-suppression products With the ever increasing intensive use of required levels. Inductive components for use on circuit boards, through-hole electronic equipment Electromagnetic are very effective in blocking interfering as well as surface-mountable. Compatibility (EMC) has become an signals, especially at high frequencies. important issue. Since 1928 laws specify The demand for SMD-suppression limits of the level of interference caused Capacitors are used as shunt impedance components is still growing.Therefore by equipment (EME Electromagnetic (ZP) for the unwanted signal. FERROXCUBE has focused its effort Emission) and also the sensitivity of Unfortunately for high frequencies, most and expertise to develop new types and equipment to incoming interference capacitors do not have the low impedan- sizes through a continuously optimized (EMS Electromagnetic Susceptibility). ce one might except because of parasitic design process to complete our SMD inductance or resistance (Fig. 2). selection: Limiting curves are defined by interna- tional organizations and national agen- Inductors (ZFXC) are used in series with Low profiled SMD-bead for flat cies such as CISPR, FCC in the USA, the the load impedance (ZL). Most inducti- designs VDE in Germany and VCCI in Japan. ve interference suppression compo- Since density of equipment increases, nents (choke, bead) are based upon a SMD-Current Compensated laws will become more stringent in the ferrite core. Chokes near future. EMC principles are explai- ned in figure 1. SMD-Wide Band Chokes Gapped SMD-bead for Power inductor Our recognized know-how and staff of application engineers are the basis of the technical support, which is entirely at your disposal for your comments and inquiries. Well controlled manufacturing proces- ses, automated production lines and measuring equipment and a long expe- rience in ferrites make FERROXCUBE a flexible, capable and reliable partner, able to advise and provide also custom- designed products, either completely new or similar to existing types. FERROXCUBE offers smart solutions to comply with the more and more severe EMC norms and requirements: our new SMD-components are suitable to prevent generated interference and to suppress incoming noise signals and parasitic oscillations. Figure 1. Principles of EMC 1SMD Beads and Chokes Introduction Ferrite inductors provide low impedan- ce for the wanted signal, but high impe- dance for the interfering, unwanted sig- nal (noise). The effectiveness of noise suppression is found by comparing the situation without and with ferrite inductor (see figure 3.A measure for the suppressors effectiveness is the insertion loss (atte- nuation), which is defined as the ratio of noise voltages (Ula / Ulb) across the load impedance ZL without and with Figure 2. Basic suppression circuits inductor Zfxc: Insertion loss is given by: 20 x log (Ula / Ulb) = 20 x log (1 + (Zfxc / ((Zi + (ZL)) in dB The parameter to characterize the inductor performance, independent of a circuit, is its impedance as a function of frequency (Zfxc = f (Freq)). Figure 3. Interference basic circuit with inductance